Objective-Hypofibrinolysis promotes atherosclerosis progression and recurrent ischemic events in premature coronary artery disease. We investigated the role of fibrin physical properties in this particular setting. Methods and Results-Biomarkers of recurrent thrombosis and premature coronary artery disease (CAD) were measured in 33 young post-myocardial infarction patients with angiographic-proven CAD and in 33 healthy volunteers matched for age and sex. Ex vivo plasma fibrin physical properties were assessed by measuring fibrin rigidity and fibrin morphological properties using a torsion pendulum and optical confocal microscopy. The fibrinolysis rate was derived from continuous monitoring of the viscoelastic properties after addition of lytic enzymes. Young CAD patients had a significant increase in plasma concentration of fibrinogen, von Willebrand factor, plasminogen activator inhibitor type 1, and lipoprotein(a) as compared with controls (PϽ0.05). Fibrin of young CAD patients was stiffer (Pϭ0.002), made of numerous (Pϭ0.002) and shorter fibers (Pϭ0.04), and lysed at a slower rate than that of controls (Pϭ0.03). Fibrin stiffness was an independent predictor for both premature CAD and hypofibrinolysis. Conclusions-This first detailed study of clot properties in such a group of patients demonstrated that abnormal plasma fibrin architecture is an important feature of both premature CAD and fibrinolysis rate. Key Words: acute coronary syndromes Ⅲ coagulation Ⅲ fibrinolysis Ⅲ pathophysiology Ⅲ fibrinogen Ⅲ thrombophilia T he mechanical properties of clots and their major constituent fibrin are normally finely tuned to optimize bleeding control while also minimizing their effect on atherothrombosis. 1,2 A decreased rate of fibrinolysis and increased thrombosis are generally associated with stiff clots, although such relationships are complex. 3,4 Many factors that affect clot structure have a great impact on the mechanical properties fibrin and fibrinolysis through modifications of various steps in the fibrin polymerization process and clot stabilization. 1,4,5 See page 2419Premature coronary artery disease (CAD) is associated with increased plasma levels of prothrombotic and proinflammatory biomarkers, including fibrinogen and plasminogen activator inhibitor (PAI) type 1, which are known to favor hypofibrinolysis 6 and to be independent predictors of CAD. 7,8 Epidemiological studies have also revealed a relationship between myocardial infarction (MI) and reduced permeability and increased stiffness of fibrin, especially in young post-MI patients. 9 These aspects of altered fibrin clot network architecture were not found to be attributable to classic risk factors including fibrinogen concentrations or common polymorphisms. 2 However, the relationships among premature CAD, abnormal fibrin physical properties, and hypofibrinolysis remain little explored. The lack of appropriately designed studies of the physical properties of fibrin, including simultaneous determination of viscoelastic and morphological properties o...

Abstract-The glycoprotein IIb/IIIa receptor inhibitor abciximab has been shown to facilitate the rate and the extent of pharmacological thrombolysis with recombinant tissue plasminogen activator (rtPA) in patients with acute myocardial infarction. However, the underlying mechanisms remain not fully determined. We sought to demonstrate that this facilitating effect of abciximab could be related to its potential to modify the clot architecture and the clot physical properties. Compared with fibrin-rich clots, platelets dramatically modified the in vitro properties of the fibrin network, leading to a significant increase of the permeability (K s ) and the viscoelasticity (GЈ) indexes but also leading to the appearance of platelet aggregates (surface area [S.ag]). These modifications resulted in a 2.6-fold decrease of the fibrinolysis rate when rtPA (1 nmol/L) was added before the initiation of clotting. Adding aspirin (100 g/mL) or abciximab (0.068 mol/L) before the clotting of platelet-rich clots (PRCs) lowered K s by 50% and 70%, respectively (PϽ0.01), GЈ by 41% and 66%, respectively (PϽ0.01), and S.ag by 32% and 61%, respectively (PϽ0.01). As a consequence, the lysis speed was increased by 21% with aspirin (PϽ0.01) and 45% with abciximab (PϽ0.01). However, unlike aspirin, permeation of preformed PRCs with abciximab (0.068 mol/L) decreased GЈ (37%, PϽ0.01), K s (35%, PϽ0.001) and S.ag (25%, PϭNS) and resulted in a 27% (PϽ0.01) increase of the lysis speed when abciximab and rtPA (0.2 mol/L) were simultaneously permeated. This effect was found to be time dependent and was observed only with early permeation, starting within the first 10 minutes of clotting. These changes in the physical properties of the PRC architecture suggest that fibrin is removed from the platelet-fibrin aggregates and reexposed into the surrounding fibrin network, increasing rtPA access to fibrin and therefore the fibrinolysis rate. The superiority of abciximab over aspirin in accelerating fibrinolysis of forming and preformed PRCs is related to its ability to modulate the interactions of fibrinogen and fibrin with platelets. These findings provide new mechanistic information on reperfusion therapy. by abciximab (Reopro) can restore coronary flow, 1 as shown in randomized trials combining abciximab with either primary angioplasty or thrombolysis in acute myocardial infarction. [2][3][4][5] However, the comprehensive mechanisms remain to be fully understood. In the present study, we sought to demonstrate that this effect of abciximab is related to its potential to modify platelet-fibrin(ogen) interactions, leading to changes of clot architecture and clot physical properties and facilitating pharmacological thrombolysis.For the first step in our experiments, differences between the physical properties of fibrin-rich clots (FRCs) and platelet-rich clots (PRC) were studied to delineate the mechanical impact of platelets on the fibrin network properties and their consequences for the fibrinolysis rate. The second step in our experiments evaluated ...

Abstract-Glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitors were shown recently to facilitate the rate and the extent of pharmacological thrombolysis. However, their synergistic potential with rtPA in dissolving thrombotic vaso-occlusions is not fully understood. We have therefore developed a dynamic and structural approach for analysis of fibrinolysis to assess the inhibiting effect of platelets and the facilitating effect of GPIIb/IIIa inhibitors in dissolving platelet-rich clots (PRCs). Fluorescent rtPA was used to study the architecture of PRCs, to follow the progression of the rtPA binding front, and to measure the lysis-front velocity using confocal microscopy. Fibrinolysis resistance of PRCs was related to a reduction of both rtPA binding and lysis-front velocities of platelet-rich areas compared with platelet-poor areas (2.4Ϯ0.2 versus 3.5Ϯ0.4 m/min for rtPA binding velocity, Pϭ0.04, and 1.2Ϯ0.6 versus 2.8Ϯ0.2 m/min for lysis-front velocity, Pϭ0.008, in platelet-rich and platelet-poor areas, respectively). Fibrinolysis appeared heterogeneous, leaving platelet-rich areas un-lysed. Adding pharmacological concentrations of abciximab (0.068 mol/L) or eptifibatide (1 mol/L) before clotting decreased the average surface of platelet-rich areas by 64% (Pϭ0.0005) and 72% (Pϭ0.0007), respectively. The resulting equalization of rtPA binding rate and rtPA binding-front velocity between platelet-rich and platelet-poor areas led to a 3-fold increase of the lysis-front velocity in platelet-rich areas of either abciximab-PRC (Pϭ0.006) or eptifibatide-PRC (Pϭ0.03). The overall lysis rate of treated-PRC was increased by 74% compared with control-PRC (PϽ0.01). These results demonstrate that fibrinolysis resistance of PRCs is related primarily to the heterogeneity in the clot structure between platelet-rich and platelet-poor areas. GP IIb/IIIa inhibitors facilitate the rate and the extent of fibrinolysis by improving rtPA binding velocity and, subsequently, the lysis rate in platelet-rich areas. These findings provide new insights on the synergistic potential of GP IIb/IIIa inhibitors and fibrinolytic agents. Key Words: fibrin Ⅲ platelets Ⅲ thrombolysis Ⅲ fibrinolysis Ⅲ inhibitors P latelets play a pivotal role in the fibrinolysis resistance of occluding coronary thrombi, and the benefit of lytic agents in patients with acute myocardial infarction is further improved with concomitant administration of aspirin. 1 More recently, direct inhibition of platelet interactions with fibrin-(ogen) by abciximab (ReoPro) has been shown to restore coronary flow 2 and to improve the outcome of acute myocardial infarction patients undergoing either primary angioplasty or thrombolysis. [3][4][5][6][7][8] In particular, the ability of abciximab alone to restore coronary vessel patency in 17% to 32% of the patients has been related in vitro to its potential to disaggregate preestablished platelet-rich clots (PRCs) and to limit clot extension. 9,10 However, whether these abciximab-mediated structural changes of PRCs can account for the accelerati...